Victoria Mboko's participation in the Queen's Club doubles alongside Serena Williams has been thrown into serious doubt following a distressing knee injury sustained during her singles encounter with Karolina Pliskova on Wednesday afternoon.
The 19-year-old Canadian, ranked ninth in the world, lost her footing on the grass surface behind the baseline whilst attempting to change direction, causing her to fall awkwardly in what witnesses described as almost doing the splits.
Mboko immediately clutched her left knee and cried out in pain as the crowd gasped.
Though she managed to stand unaided, the teenager was visibly distraught as she spoke with medical staff.
Victoria Mboko's injury appears to have ended Serena Williams' comeback early
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"There is no stability right now," Mboko was heard telling a physiotherapist via courtside microphones.
Trailing 6-2, 3-4 and with a break point opportunity, she retired from the match in tears, marking the first retirement of her WTA Tour career.
The injury casts significant uncertainty over Williams' highly anticipated return to competitive tennis, which began just 24 hours earlier at the London venue.
On Tuesday, the 44-year-old American partnered with Mboko to defeat third seeds Nicole Melichar-Martinez and Erin Routliffe 7-6 (2), 6-2 in what was Williams' first professional match since the 2022 US Open.
Victoria Mboko suffered a severe injury that forced her into tears
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The pair were due to face Leylah Fernandez and Laura Siegemund in Thursday's quarter-final, but that fixture now hangs in the balance.
Tournament organisers have yet to confirm whether a replacement partner could be arranged should Mboko be unable to continue.
Williams had also announced plans to compete in doubles at the Berlin Open next week, though those arrangements may similarly be affected by her partner's condition.
Pliskova, who progressed to the quarter-finals following Mboko's withdrawal, expressed sympathy for her young opponent.
"It's such a shame. I think we played quite a good game and she was improving as the match was going on," the Czech player said.
Serena Williams returned to tennis after 1,376 days on Tuesday
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"I wish her only the best. It's not the way I want to win so hopefully she is going to be fine for Wimbledon."
The pre-Wimbledon grass-court event had been the stage for Williams' eagerly awaited comeback after nearly four years away from professional competition.
The 23-time Grand Slam singles champion last competed at the 2022 US Open before stepping away from the sport.
Fans and fellow players have offered messages of support for Mboko, with the tennis world now awaiting updates on her condition ahead of Thursday's scheduled doubles fixture.